An example of various types of control units for a multiphase rotary electric machine is configured to carry out PWM (Pulse Width Modulation) control. Specifically, during the PWM control, the control unit compares a request current wave required to output a request torque with a carrier triangle wave, and generates a plurality of voltage pulses in every cycle of the request current wave based on the comparison result. These voltage pulses allow switching elements of an inverter in a bridge configuration to be turned on and off, thereby generating an output sinusoidal current corresponding to the request current wave.
The PWM control of the inverter however increases power loss during high output torque and/or high revolutions of the multiphase rotary electric machine because of switching losses of the switching elements. For this reason, during high output torque and/or high revolutions of the multiphase rotary electric machine, the control unit can carry out single pulse control.
Specifically, during the single pulse control, the control unit generates a single voltage pulse in every half cycle of the request current wave to be applied to each of the switching elements, and controls the generated single voltage pulse in phase depending on a rotational phase of the rotor of the multiphase rotary electric machine.
The single pulse control of the inverter can not only prevent an increase in power loss during high output torque and/or high revolutions of the multiphase rotary electric machine but also improve the voltage utilization factor of the multiphase rotary electric machine. Note that the voltage utilization factor can be calculated by dividing an RMS value of a line-to-line voltage of the multiphase rotary electric machine by an input voltage of the inverter.
Note that, as another method for effectively addressing an increase in power loss during high output torque and/or high revolutions of a multiphase rotary electric machine, Japanese Unexamined Patent Publication H07-111777 discloses a method of controlling an instantaneous one phase current based on a delay time thereof.